Nitration of cellulose



Patented Nov. 28, 1922.

v UNITED STATES-PATENT OFFICE.

ROBERT P. CALVERT, OF MONTCLAIR, NEW JERSEY, ASSIGNOR TO E.I. Di: FONT m;

NEMOURS & COMPANY, OF WILMINGTON, DELAWARE, A CORPORATION OF DELA- WARE.

m'raa'r on or cnLLULosE.

No Drawing. Application filed November To all whom it may concern:

Be it known that I, ROBERT P; CALVERT, a citizen of the United States, and a resident of Montclair, in the county of Essex and State of New Jersey, have invented a certain new and useful Nitration of Cellulose, of which the following is a specification.

This invention relates to a process of nitrating cellulose, and pertains particularly to the nitration of tissue paper so treated as to lessen the amount of nitrating acids retainable thereby as a result of capillarity or surface action.

In the nitration'of cellulosic materials, there is lost a certain amount of acid through chemical combination with the cellulose and additional amounts in the form of fumes and of acid retained mechanically by the cellulose after wringing. When the cellulose is nitrated in the form of tissue 'paper .this loss ofacid through mechanical retention is especially large. I

I have found that by compressing the tissue paper, as bypassing it through calenders or super-calenders,the amount of acid it will retain mechanically after vnitration has been completed is much less than if uncompressed tissue paper had been used.

The compression to which the tissue paper should be subjected by the calenders should be'suificient to substantially reduce its thickness. I 'preferably-compress the paper to approximately half of its former thickness.

The expression tissue paper is meant to cover any kind of thin paper into which cellulose is made before nitration. As an example, there may be used tissue paper which is made by pulping rag cuttings with water and then forming the pulp into paper of thickness approximately .0022 and having a weight of 13 to 15 pounds per ream.

v A specific example of the process follows: Tissue paper such as is made from cotton rags is compressed to about half its former thickness bypassing it through calenders or super-calenders, is shredded into small pieces, and is then dried to a. moisture content of 5% orless. Twenty pounds of the dried paper is then fed into an iron pot containing 1200 lbs. of mixed acid of the approximate composition of 60% sulfuric acid, "20% nitric acid and 20%- water. After thirty minutes contact between the acid and ing a thin 13, 1919, Serial No. 337,847. Renewed February 23, 1922. Serial No. 538,773.

the paper, the entire chargeis dumped into a centrifugal which serves to remove most of the acid. The remaining acid is removed I by washing.

Analysis of the mixed and spent acids combined chemically or retained mechanically by the nitrocellulose are about as follows, comparison being made with pyroxylin made from compressed and from uncompressed paper Acid combined chemically and retained mechanically by It will thus be seen that the saving in 0011 centrated acid is about four-tenths of a pound for each pound of nitrocellulose produced.

I claim:

1. The process of nitrating cellulose which comprises subjecting a thin sheet of cellulose to high compression, shredding the cellulose sheet and treating it with a nitrating acid mixture.

2. The process of nitrating tissue paper which comprises passing it through calenders under a pressure sufficient to materially reduce its thickness, and subjecting the compressed paper to the action of a nitrating acid mixture.

3. The process of nitrating tissue paper which comprises passin it through calenders under a pressure su1cient to materially reduce its thickness, shredding it into small pieces, drying it to a moisture content of not more than 5%, treating it with an excess of a nitrating mixture of sulfuric and nitric acids, centrifugally separating as much strong acid from the nitrated paper as is practicable, and then removing acid remaining in the nitrated paper by washing.

4. In the process of nitrating cellulose, the preliminary step which comprises subjectsheet of said cellulose to high compression.

' 5. In the process of nitrating tissue paper,

the step which comprises subjecting said paper to a compression sufiicient to matethe steps which comprise passing said paper rially reduce its thickness. through calenders under such pressure as to 10 6. In the process of nitrating tissue paper, reduce it to about half its former thickness, the step which comprises passing said paper and then shredding the compressed paper 5 through'ralenders under such pressure as into small pieces.

to reduce it to about half its former thick- In testimony whereof I afiix my signature. ness.

T. In the process of nitrating tissue paper, ROBERT P. CALVERT. 

